Modern fuel delivery systems for automotive vehicles with engines having fuel injectors have utilized an electrically driven fuel pump in the vehicle main fuel tank. Typically, the electric fuel pump is mounted either directly in the vehicle tank, or is mounted within a reservoir canister received in the tank as shown for example in U.S. Pat. Nos. 4,747,388; 4,807,582; 4,831,990; 4,893,647; and 4,964,787. The canister reservoir supplies fuel to the pump in the event there is an interruption in the availability of fuel from the tank, such as when, under low fuel level conditions, cornering of the vehicle causes sloshing or movement of the fuel away from the pump inlet and to one side or the other of the tank, and/or when the tank is excessively tilted by vehicle inclination on severe grades, or when essentially all of the fuel in the main tank has been consumed or used. Typically, the output of the fuel pump is greater than that required by the vehicle engine and the excess fuel is either returned from the fuel injectors to the tank or to the in-tank canister reservoir.
Typically, in a no-return fuel system, there is only one fuel supply line between the fuel pump module and an engine fuel rail or manifold distributing fuel to the individual fuel injectors, and downstream of the fuel injectors there is no line returning unused fuel from the rail or manifold to the fuel tank. In such non-return fuel systems excess fuel is bypassed directly to the tank or canister reservoir, typically by a pressure regulator usually located closely downstream of the pump outlet within the tank or canister, or by a return line to the tank or canister when the regulator is exteriorly remote from the tank.
Generally speaking two types of electrically driven rotary fuel pumps have hitherto been used in the vehicle main fuel tank for pumping liquid fuels to the fuel injectors of the automotive vehicle engine, namely a turbine type vane pump or a positive displacement pump. One preferred form of a positive displacement gear rotor type electric fuel pump is disclosed in U.S. Pat. No. 4,697,995, and a suitable turbine regenerative fuel pump is disclosed in U.S. Pat. No. 5,257,916.
Such in-tank vehicle fuel pumps must be capable of operating in a wide range of ambient temperatures. It is necessary that a low pressure be created in the entry to the pump chamber in order to draw fuel into the pumping chamber. This reduced pressure alone may cause a change in state of the fuel from liquid to vapor at elevated temperatures and significantly reduce the efficiency of the pump.
In another condition as, for example, when a vehicle has been operating and then the engine shut off for a period, the fuel line between the pump and fuel injectors full of liquid fuel under pressure whereas the fuel in the pump can be completely vaporized due to the elevated temperature in the fuel tank and pump itself. Thus, when the engine is restarted, the pump is full of vapor and even the fuel in the entrance filter may be vaporized. The pump cannot, under these conditions, generate enough pressure to move the fuel in the pressurized fuel supply line.
Accordingly, both of the aforementioned U.S. Pat. Nos. 4,697,995 and 5,257,916 disclose a rotary pump construction with a built-in vapor purging system which will enable the pump to operate under the conditions above described without interruption of the fuel supply, with one major exception. However, in accordance with the present invention it has been found that a turbine type vane pump when disposed within an in-tank canister reservoir does not operate satisfactorily to sufficiently purge itself of vapor under adverse temperature or other vapor-inducing conditions. Due to the preferred location and size of the vapor purge port in the first or pre-channel zone and the inherent operating characteristics of the turbine pump, only a small amount of vapor pressure build up can be produced by such a pump at the pump vapor purge port. Hence, unlike the positive displacement pumps employed within the in-tank canister reservoirs, it has been found that such a vane type pump cannot purge itself of vapor in the pumping channel if the pressure differential between the pump inlet and the vapor port outlet exceeds about 21/2 inches of water.
This constraint as to self-purging of vapor does not apply to positive displacement gear rotor pumps of the aforementioned type since they characteristically pump both fuel vapor and air very well. Hence, when mounted inside an in-tank fuel reservoir canister and provided with a vapor purging port communicating with the column of fuel in the canister and located at approximately the elevation of the rotary pump chamber, such positive displacement pumps can purge vapor into the canister against a gravity fuel differential pressure head ranging from say six on up to ten or twelve inches, as when the canister reservoir is full and the gravity head at the pump inlet exerted by the body of fuel in the tank exterior to the canister reservoir is very low.
Nevertheless, some OEM automotive vehicle manufacturers have preferred turbine vane fuel pumps for use in fuel tanks over gear rotor positive displacement pumps for a variety of reasons, even though they have had to forsake the advantages of a canister reservoir-type reserve supply of fuel for preventing starvation of fuel supply to the turbine pump from the main tank in order to obtain vapor self-purging operation. In an attempt to make up for this lack of the preferred selectable alternative canister reserve supply of fuel, such as that provided in U.S. Pat. Nos. 4,747,388, some automotive manufacturers have mounted turbine vane fuel pumps in specially configured fuel tanks with the pump inlet submerged in a so-called "swirl pot", i.e., a molded-in basin in the tank bottom in an attempt to maintain an adequate body of fuel in the vicinity of the fuel pump inlet to prevent pump starvation. However such swirl pots are still subject to being emptied by severe vehicle cornering or excessive vehicle inclination, as well as when essentially all of the fuel of the main tank has been consumed or used. Such swirl pots also inherently must be limited in their length, width and depth dimensions, thereby imposing a further constraint on the bulk of the fuel pump and associated filter package which can be accommodated in such swirl pots.
Despite such hitherto prevailing limitations, some OEM automotive vehicle manufacturers have preferred to use turbine vane-type fuel pumps over gear rotor positive displacement pumps for in-tank mounting because such turbine vane pumps generally are quieter and smoother running, and also have low tank fuel level operation performance characteristics preferred by such vehicle manufacturers over those of gear rotor positive displacement pumps. With a typical positive displacement gear rotor fuel pump, such as that disclosed in the aforementioned U.S. Pat. No. 5,257,916, when the pump encounters like conditions with a large presence of vapor in the pump chamber, the positive displacement pump will continue to pump liquid fuel but will also pump vapor as well. When this condition occurs the fuel pumped to the engine contains vapor and/or air entrained with liquid fuel. This will cause the vehicle engine to spit and stumble or otherwise run rough even though the engine continues to run on this vapor and liquid fuel mixture. However, because of constraints imposed by engine control unit (ECU) operational characteristics and exhaust emission requirements, several vehicle manufacturers would prefer to see the instantaneous shut off characteristic under extreme low tank fuel level conditions of the turbine vane fuel pump, wherein the pump ceases pumping any fuel.